Home theater systems provide a number of components, which may be located in various parts of the room. The components include the home theater receiver/amplifier, front stereo speakers (left and right), rear surround sound speakers (left and right), a center speaker, and a subwoofer. Various other combinations of speakers may also be used, including additional or fewer speakers.
One problem with such systems is that a major aspect of acoustical sound reproduction may depend upon the relative location of each of the speakers in a room, relative to the preferred listening area, as well as room acoustics, speaker orientation, and the like. These aspects are largely outside the control of the manufacturer, as speaker placement can only be suggested by the manufacturer, and room configuration or other criteria may alter such placement by the consumer. In addition, the size of a room in which the system is setup is impossible to predetermine, and thus a great variance results in the placement, orientation, and location of speakers, as well as their relative distance from the preferred listening area.
One Prior Art approach for high-end home theater systems has been to hire a skilled acoustician to setup the home theater system. Such a skilled technician can adjust the location and placement of the speakers, and using various components (adjustable delays, equalizers, and even passive acoustical components) optimize the sound quality for a particular room. Unfortunately, hiring an acoustician to fine tune their home theater system is expensive while many “consumer grade” home theater systems sell for only a few hundred dollars, which is far less than the cost of even one in-home visit by an acoustician.
Another approach has been to provide a built-in system for measuring the relative time delay (e.g., location) of speakers within a room using a microphone and some processing equipment so that a consumer can calibrate the system for a given room. Such a system has many advantages, as it reduces the overall cost of installation, provides a better acoustical response to the system (resulting in fewer consumer complaints) and also allows the system to be easily moved to new locations.
While a number of such systems exist in the present market, one such system is illustrated, for example, by Ohta, U.S. Pat. No. 6,655,212, issued on Dec. 2, 2003 (hereafter “Ohta”), and incorporated herein by reference. FIG. 1 is a diagram from Ohta, illustrating a configuration of a measurement system including the sound field measuring apparatus. Measurement system 100 comprises a number of components. DSP (Digital Signal Processor) 1 outputs a test signal to D/A converters 2a, 2b, etc. Amplifiers 3a, 3b, etc. receive signals output from D/A converters 2a, 2b, etc. and drive speakers 4a, 4b, etc. Microphone 6 is disposed at a predetermined position (listening position) in an acoustic space 5 where the speakers 4a, 4b, etc. are placed. Amplifier 7 amplifies a signal output from microphone 6 and outputs the signal to A/D converter 8.
DSP 1 includes a number of components. Exponential pulse generator 11 generates an output signal to speaker (“SP”) selector 12, which in turn outputs the signal to a selected one (or more) of D/A converters 2a, 2b, etc. RAM 14 stores a received signal from A/D converter 8. Calculation section 15 uses the data stored in RAM 14 to calculate the time of arrival of an exponential pulse transmitted via speaker 4a, 4b, etc. Control section 13 operates exponential pulse generator 11 and RAM 14 so as to synchronize start timings. Calculation section 15 includes a rising emphasizing section 151, a time detecting section 152, and a calculating section 153.
Although not shown, DSP 1 has a signal processing circuit, which, during multi-channel audio reproduction using the speakers 4a, 4b, etc., delays each channel's signal by a predetermined time period. According to this configuration, the perceived distances between the speakers and the listening position can be made constant by adjusting the time delays to compensate for the actual differences in distance.
In operation, a system such as that illustrated in FIG. 1 may send a signal generated by exponential pulse generator 11 (or other sound source) to a speaker 3a, 3b, etc. via speaker-selector 12. Microphone 6 maybe positioned by a consumer at a preferred listening location in the room. Microphone 6 receives the exponential pulse (or other sound) from speaker 3a, 3b, etc. and transmits this signal, via amplifier 7 and A/D converter 8 to RAM 14. Calculating section 15 may then measure the time delay between the output of the sound pulse from speaker 4a, 4b, etc. and the reception at microphone 6, and thus calculate the relative distance of the speaker from the preferred listening position. This value may be displayed to the user as a physical distance, and/or may be used as a time delay value internally. Each speaker 4a, 4b, etc. is tested in turn and relative time delays calculated. The home theater system can then adjust the relative time delays of each speaker accordingly to provide optimal sound levels at the preferred listening area.
Thus, a home theater system may employ an “auto-setup” mode to determine speaker distance from a preferred listening location to set internal delays. The delay measurement may be measured by detecting the impulse response of the system through a variety of means (direct, Maximum Length Sequence (MLS), adaptive filter, and the like.). Such techniques for measuring the impulse response are known in the art. For example, Borish and Agell, “An Efficient Algorithm for Measuring the Impulse Response using Pseudorandom Noise”, J. Audio Eng. Soc., Vol. 31, No. 7, July/August 1983, incorporated herein by reference, and Rife and Vanderkooy, “Transfer-Function Measurement with Maximum-Length Sequences”, J. Audio Eng. Soc., Vol. 27, No. 6, June 1989, incorporated herein by reference, disclose how Maximum Length Sequences (MLS) can be used to measure the impulse response of a linear system.
In Prior Art audio and home theater systems, the location of the initial peak of the impulse response (delay) has been used to determine the distance of the speaker from a microphone placed at a preferred listening location. When measuring a subwoofer, however, the peak of the impulse response does not always accurately reflect the distance of the subwoofer from the preferred listening location due to the band-limited response of the speaker. Additionally, many subwoofers include a built-in low-pass crossover that further alters the impulse response and thus provides an inaccurate distance measurement.
FIG. 2 is a graph illustrating an example of the first peak of four impulse responses for different subwoofer settings. All four of the peaks were measured using the same test setup with a subwoofer 87 inches from a microphone in a typical room. The y-axis represents relative power levels as measured during testing. The x-axis represents the time delay of the initial peak, as measured in samples at a sample rate of 6 kHz.
The four lines, working from left to right, correspond to different subwoofer settings as follows. Line 110 represents the first peak response with the subwoofer crossover disabled. Line 120 represents the peak response with the subwoofer crossover set to 150 Hz. Line 130 represents the peak response with the subwoofer crossover set to 100 Hz. Line 140 represents the peak response with the subwoofer crossover set to 50 Hz.
In the graph of FIG. 2, peak 110, with the crossover disabled, most accurately reflects the location of the subwoofer from the microphone (e.g., approximately 87 inches). Succeeding peaks are located much further from the actual distance value. With the crossover set to 50 Hz, the peak of the impulse corresponds to a distance almost four feet from the actual location of the subwoofer. Inaccurate measurement of the subwoofer location hampers proper setup of the home theater system, as the subwoofer sound may not be optimized for the preferred listening location.
Prior Solutions to this problem have been varied. In some applications, manufacturers simply ignore the problem, as they have no ready fix. This approach is obviously not an adequate solution. Other manufacturers instruct the consumer to disable the subwoofer crossover network, or set it to its highest frequency setting. Unfortunately, many subwoofers do not allow the crossover to be disabled and/or do not have an adjustable frequency setting. In addition, even if the subwoofer were so equipped, a consumer would have to know how to perform such a procedure and take the extra step when calibrating the system and remember to reset the subwoofer when completed.
Another solution is to insert a so-called “fixed fudge-factor.” When measuring a subwoofer, a fixed value is subtracted from the result to approximate the correct location of the subwoofer. In the example illustrated in FIG. 2, adding such a “fixed fudge factor” could change the error from +4 feet to +/−2 feet, depending upon subwoofer crossover settings. Obviously, this approach is also very limited.
Thus, it remains a requirement in the art to provide a technique for measuring distance (delay) for a subwoofer or other speaker whereby the crossover settings of the speaker do not need to be changed or known in order to accurately measure the location of the speaker.